Early preplant application timing effects on acetamide efficacy in no-till corn (Zea mays)

Metolachlor, dimethenamid, acetochlor, and a commercial premixture of flufenacet plus metribuzin were applied 60, 45, 30, and 15 d before planting (DBP) and at planting (preemergence [PRE]) at Dekalb and Urbana, IL in 1995 and 1996. The soil types were a Drummer silty clay loam (fine-silty, mixed, superactive, mesic Typic Endoaquoll) with 2.8% organic carbon and a pH of 6.5 at Dekalb and a Flanagan silt loam (Fine, smectitic, mesic Aquic Argiudoll) with 2.0% organic carbon and a pH of 6.2 at Urbana. Herbicide and application timing affected giant foxtail control and densities. Neither herbicide nor application timing affected crop injury or grain yield. Test of the main effects showed that metolachlor and flufenacet plus metribuzin were more effective than acetochlor or dimethenamid in controlling giant foxtail at 30 and 60 d after planting (DAP) and in reducing foxtail density at 60 DAP. Giant foxtail control 60 DAP was greater than 80% for both metolachlor and flufenacet plus metribuzin for all application timings. Dimethenamid and acetochlor applied at 60 and 45 DBP provided less giant foxtail control when compared with metolachlor and flufenacet plus metribuzin applied at the same time. All herbicides provided greater than 90% giant foxtail control at the PRE application timing. Giant foxtail control provided by metolachlor and flufenacet plus metribuzin was insensitive to application timing from 60 DBP to PRE, whereas both dimethenamid and acetochlor efficacy was lowered when applied between 30 and 60 DBP.